Method for detecting electronic lighting flickering

ABSTRACT

A method for detecting electronic lighting flickering includes: taking a video of an electronic light with a duration of a predetermined period and a scanning frequency; extracting a predetermined number of frames of pictures from the video; determining a flickering frequency of the electronic light; determining at least one fixed reference point at each frame; and reconstructing a brightness waveform of the electronic light from the reference point in all frames of the video.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. non-provisional patentapplication Ser. No. 62/100,909 filed on Jan. 8, 2015; the contents ofwhich is hereby incorporated by reference.

FIELD OF THE PATENT APPLICATION

The present patent application generally relates to electronic lightingtechnologies and more specifically to a method for detecting electroniclighting flickering.

BACKGROUND

In old times, incandescent light bulb is a major lighting equipment. Butits efficiency is low. Lots of energy is wasted in the form of heat. So,the global trend of the lighting equipment is from incandescent bulb toCFL bulb, and then to LED bulb. The CFL bulb includes mercury which istoxic. The LED bulb is most energy efficient but there exists a LEDflickering problem.

For incandescent bulbs and CFL bulbs, the light tube also has lightflickering, but the problem for LED bulbs is more serious. If people areexposed to bulb which has invisible frequency (high frequency) flicker,it will trigger malaise, headaches and impaired visual performance.Also, if people are exposed to visible frequency (low frequency)flicker, it will trigger epileptic seizure, headaches and impairedvisual performance.

Nowadays, a LED lamp is becoming a very common type of lightingequipment. If the user has a simple way to distinguish the extent of LEDflickering, they can avoid using the lamp which is harmful to theirhealth.

An actual lamp produces flickers which are rapid and repeated changesover time in the brightness of light, i.e. brightness waveform with afixed frequency. For LED lamps, it is caused from the rapid and repeatedchange over time in current of its driver, which is an unavoidablephenomenon.

SUMMARY

The present patent application is directed to a method for detectingelectronic lighting flickering. In one aspect, the method includes:taking a video of an electronic light with a duration of a predeterminedperiod and a scanning frequency; extracting a predetermined number offrames of pictures from the video; determining a flickering frequency ofthe electronic light based on number of pixels between two consecutivebight lines in each frame, number of pixels across the frame, and timeperiod for which the frame is captured; determining at least one fixedreference point at each frame; reconstructing a brightness waveform ofthe electronic light from the reference point in all frames of the videobased on brightness value of the reference point in each frame and timelocation value of the reference point in each frame; and determiningrelationship between the flickering frequency of the electronic lightand the scanning frequency of the video. If the flickering frequency isa multiple of the scanning frequency, the video is retaken with adifferent scanning frequency. If both the flickering frequency and thescanning frequency are multiples of a same number, additional videos ofthe electronic light are taken or number of the reference points isincreased.

The flickering frequency of the electronic light may be determined basedon a flickering period, the flickering period being determined based onratio of the number of pixels between two consecutive bright lines ordark lines in each frame and the number of pixels across the frame,multiplied by the time period for which the frame is captured. The timelocation value of the reference point in each frame may be determinedbased on ratio of number of pixels between the reference point and abright line next to the reference point and the number of pixels betweentwo consecutive bight lines in the frame, multiplied by the flickeringperiod.

If additional videos of the electronic light are taken, starting pointof the brightness waveform of one video may be different from that ofanother video.

In another aspect, the present patent application provides a method fordetecting electronic lighting flickering. The method includes: taking avideo of an electronic light with a duration of a predetermined periodand a scanning frequency; extracting a predetermined number of frames ofpictures from the video; determining a flickering frequency of theelectronic light; determining at least one fixed reference point at eachframe; and reconstructing a brightness waveform of the electronic lightfrom the reference point in all frames of the video.

The flickering frequency of the electronic light may be determined basedon number of pixels between two consecutive bight lines in each frame,number of pixels across the frame, and time period for which the frameis captured.

The flickering frequency of the electronic light may be determined basedon a flickering period, the flickering period being determined based onratio of the number of pixels between two consecutive bright lines ordark lines in each frame and the number of pixels across the frame,multiplied by the time period for which the frame is captured.

The brightness waveform of the electronic light may be reconstructedfrom the reference point in all frames of the video based on brightnessvalue of the reference point in each frame and time location value ofthe reference point in each frame. The time location value of thereference point in each frame may be determined based on ratio of numberof pixels between the reference point and a bright line next to thereference point and the number of pixels between two consecutive bightlines in the frame, multiplied by the flickering period.

The method for detecting electronic lighting flickering may furtherinclude determining relationship between the flickering frequency of theelectronic light and the scanning frequency of the video. If theflickering frequency is a multiple of the scanning frequency, the videomay be retaken with a different scanning frequency.

If both the flickering frequency and the scanning frequency aremultiples of a same number, additional videos of the electronic lightmay be taken. If both the flickering frequency and the scanningfrequency are multiples of a same number, number of the reference pointsmay be increased.

In yet another aspect, the present patent application provides a methodfor detecting electronic lighting flickering. The method includes:taking a video of an electronic light with a duration of a predeterminedperiod and a scanning frequency, the video including a predeterminednumber of frames of pictures; determining a flickering frequency of theelectronic light; determining at least one fixed reference point at eachframe; determining relationship between the flickering frequency of theelectronic light and the scanning frequency of the video; andreconstructing a brightness waveform of the electronic light from thereference point in all frames of the video based on the determinedrelationship.

The flickering frequency of the electronic light may be determined basedon number of pixels between two consecutive bight lines in each frame,number of pixels across the frame, and time period for which the frameis captured. The flickering frequency of the electronic light may bedetermined based on a flickering period, the flickering period beingdetermined based on ratio of the number of pixels between twoconsecutive bright lines or dark lines in each frame and the number ofpixels across the frame, multiplied by the time period for which theframe is captured.

The brightness waveform of the electronic light may be reconstructedfrom the reference point in all frames of the video based on brightnessvalue of the reference point in each frame and time location value ofthe reference point in each frame. The time location value of thereference point in each frame may be determined based on ratio of numberof pixels between the reference point and a bright line next to thereference point and the number of pixels between two consecutive bightlines in the frame, multiplied by the flickering period.

If the flickering frequency is a multiple of the scanning frequency, thevideo may be retaken with a different scanning frequency. If both theflickering frequency and the scanning frequency are multiples of a samenumber, additional videos of the electronic light may be taken or numberof the reference points may be increased.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 shows an exemplary current waveform of a LED driver.

FIG. 2 shows an exemplary brightness waveform of light flickering of aLED light.

FIG. 3 shows another exemplary brightness waveform of light flickeringof a LED light.

FIG. 4 shows a current waveform of a LED driver.

FIG. 5 shows dark and bright lines of light flickers in photos or videosrecorded by a mobile phone camera.

FIG. 6a shows an exemplary frame of a video of a LED light.

FIG. 6b shows another exemplary frame of a video of a LED light.

FIG. 6c shows yet another exemplary frame of a video of a LED light.

FIG. 7 shows a fixed reference point A and a fixed reference point B ina frame of a video of a LED light recorded by a smartphone camera.

FIG. 8 shows a brightness waveform constructed from Y number ofbrightness and time location values of point A.

FIG. 9 shows a light flickering waveform where a smartphone camera takesFrame 1 and Frame 2.

FIG. 10 shows a light flickering waveform where a smartphone cameratakes Frames 1-6.

FIG. 11 shows a light flickering waveform where a smartphone cameratakes Frames 1-6, in which the starting point of the brightness waveformis different from the waveform in FIG. 10.

FIG. 12 shows light flickering waveform where a smartphone camera takesFrames 1-31.

FIG. 13 is a flow chart illustrating a method for detecting electroniclighting flickering in accordance with an embodiment of the presentpatent application.

FIG. 14 illustrates that the period of a brightness waveform can becalculated by calculating the ratio of the pixel number of “a” and thepixel number of “b” and times it by 1/30 s.

FIG. 15 shows five fixed reference points next to a light bulb in aframe.

FIG. 16 illustrates reconstruction of a brightness waveform of lightflickering of a LED light.

DETAILED DESCRIPTION

Reference will now be made in detail to a preferred embodiment of themethod for detecting electronic lighting flickering disclosed in thepresent patent application, examples of which are also provided in thefollowing description. Exemplary embodiments of the method for detectingelectronic lighting flickering disclosed in the present patentapplication are described in detail, although it will be apparent tothose skilled in the relevant art that some features that are notparticularly important to an understanding of the method for detectingelectronic lighting flickering may not be shown for the sake of clarity.

Furthermore, it should be understood that the method for detectingelectronic lighting flickering disclosed in the present patentapplication is not limited to the precise embodiments described belowand that various changes and modifications thereof may be effected byone skilled in the art without departing from the spirit or scope of theprotection. For example, elements and/or features of differentillustrative embodiments may be combined with each other and/orsubstituted for each other within the scope of this disclosure.

In the embodiments below, the method for detecting electronic lightingflickering is directed to a LED light. It is understood the method canbe applied to other forms of electronic lighting with periodicalflickering. FIG. 1 shows an exemplary current waveform 101 of a LEDdriver. The current waveform 101 has a fixed period. The LED flickerprofile (brightness waveform of LED lamp produced) is the same as thecurrent waveform 101. The flicker frequency is also exactly the same asthe current frequency.

FIG. 2 shows an exemplary brightness waveform 201 of light flickering ofa LED light. Flicker percentage, flicker index and flicker frequency arethe metrics used to describe how severe the light flicker is. The higherthe flicker percentage and flicker index, the more severe the lightflicker is, wherein:Flicker frequency=1/periodFlicker percentage=(max−min)/(max+min)×100%

FIG. 3 shows another exemplary brightness waveform 301 of lightflickering of a LED light. Referring to FIG. 3, Flicker index=Area abovemean/Total Area=Area 1/(Area 1+Area 2).

According to an embodiment of the present patent application, thebehavior (bright lines and dark lines) of light flickering produced inphoto or video recorded by a digital or smartphone camera is used tofind out the exact brightness waveform of light flicker and thuscalculate the values of the flicker metrics.

Light flicker frequency can be found from a photo or a frame of a video.Smartphone camera usually takes 1/Y s to capture a photo or a frame of avideo. Actually, the whole photo or frame is not captured in the samemoment, but by column to column (rolling shutter technique). As thebrightness of lamp varies due to light flicker, bright lines and darklines appear in photo or frame.

In FIG. 5, the brightness pattern (bright lines and dark lines) in photochanges from right to left and matches with the current waveform patternof the LED driver in FIG. 4, and in turn, matches with the brightnesswaveform of light flicker. As a result, by finding the ratio of thepixel number between two consecutive bright lines (501 and 503) and thepixel number across the photo or frame 505, and times it by 1/Y s, theperiod of the light flicker can be found.Light flicker period=(1/Y)×(pixel no. between two consecutive bright ordark lines/total pixel no. across the photo or frame)Light flicker frequency F=1/light flicker period

In this embodiment, as aforementioned, the flickering frequency of theelectronic light is determined based on a flickering period, which isfurther determined based on ratio of the number of pixels between twoconsecutive bright lines (501 and 503) or dark lines in each frame andthe number of pixels across the frame, multiplied by the time period(1/Y) for which the frame is captured.

Brightness waveform can be found from a video. Take 1 s of video from asmartphone camera. That is video has Y number of frames. The brightnesspattern (bright lines and dark lines) of the frames are shifting fromframe to frame, referring to frames in FIGS. 6a, 6b and 6c . In each ofthe frames, define a fixed reference point A, referring to FIG. 7.

Next, get the brightness value of point A in each frame. In addition,find the time location value of point A in the corresponding period ineach frame. This can be done by calculating the ratio between the pixelnumber of t and s, and then times it by the light flicker period,referring to FIG. 7.

As a result, Y brightness values and Y corresponding time locationvalues from the Y number of frames are obtained. The brightness waveformof light flicker can be reconstructed by the Y brightness and timelocation values, referring to FIG. 8.

In this embodiment, as aforementioned, the time location value of thereference point in each frame is determined based on ratio of number ofpixels between the reference point and a bright line next to thereference point (corresponding to “t”) and the number of pixels betweentwo consecutive bight lines in the frame (corresponding to “s”),multiplied by the flickering period.

If the Y brightness and time locations values of point A are notsufficient enough to reconstruct the brightness waveform, another fixedpoint B (referring to FIG. 7) in each of the frames can be defined andanother set of Y number of brightness and time location values isobtained. Thus 2 times Y number of brightness and time location valuesare used to reconstruct the brightness waveform after doingnormalization of point A and point B. Moreover, more and more fixedpoints C, D, E, F, etc can be further defined.

In this embodiment, the Y number of brightness and time location valuesof point A, i.e. (A1, t1), (A2, t2) . . . , (AY, tY), will sometimesrepeat. For examples, (A1, t1) value may be the same as (A4, t4) value.It is due to the relationship between the video scanning frequency f ofthe smartphone camera and the light flicker frequency F.

Case 1: If the light flicker frequency F is a multiple of the videoscanning frequency f, then (A1, t1)=(A2, t2)=(A3, t3)= . . . =(AY, tY).Suppose f is 30 Hz and F is 120 Hz. In the first 1/30 s, the mobilephone camera will take 1 frame, and light flicker waveform will pass 4periods, i.e. 4 sets of bright and dark lines. In the second 1/30 s, themobile phone camera will take a second frame, and the light flickerwaveform will pass second 4 periods. The brightness and time locationvalue of point A stays the same all the time, referring to FIG. 9.

Reconstructing the brightness waveform of the light flicker may not beperformed by only a single brightness and time location value (A1, t1).This problem can be solved by changing the video scanning frequency f ofthe smartphone camera so that the light flicker frequency F is not amultiple of it anymore.

Case 2: If the light flicker frequency F is not a multiple of the videoscanning frequency f, but both of them can be divided by a constantnumber, in other words, both of them are multiples of the same number,then the brightness and time location values start to repeat itselfafter n number of frames. Suppose f is 30 Hz and F is 50 Hz,

F/f=50/30;

F/f=5/3 (both of them are divided by a constant number “10”);

the denominator is “3”, which means that for the first 3 frames, thebrightness and time location values are different. But after the 3frames, they will start to repeat, referring to FIG. 10.

Reconstructing the brightness waveform of the light flicker may not beperformed by only 3 sets of brightness and time location values of thepoint A. This can be solved by getting more brightness and time locationvalues by:

-   -   1. Defining a lot of fixed points (B, C, D, E, etc.) rather than        just a single point A.    -   2. Taking more videos, because the starting point of the        brightness waveform of light flicker may shift in each video. As        shown in FIG. 11, this is the second video, in which the        starting point of the brightness waveform is different from        video 1 in FIG. 10.

Case 3: If the light flicker frequency F is not a multiple of the videoscanning frequency f, and both of them cannot be divided by a constantnumber, then (A1, t1), (A2, t2) . . . (AY, tY) will not repeat. Supposef is 31 Hz and F is 50 Hz, F/f=50/31. The denominator is “31”, whichmeans that for the 31 frames, the brightness and time location valuesare different. The brightness waveform of the light flicker can bereconstructed by the 31 brightness and time location values of thesingle point A, referring to FIG. 12.

FIG. 13 shows the overall steps on how to reconstruct the brightnesswaveform by taking video of a light flicker. The steps will be describedin details according to the following example.

Step 1301: Take 1 s of video

As shown in FIG. 13, a smartphone camera is used to take 1 s of videofor a bulb. The video scanning frequency f of the smartphone camera is30 Hz. Bright lines and dark lines appear in the video and they areshifting from frame to frame.

Step 1303 and Step 1305: Extract 30 frames from the video and find thelight flicker frequency F. As shown in FIG. 14, one frame from the videocan be selected to calculate the period of the brightness waveform. Itis done by calculating the ratio of the pixel number of “a” and thepixel number of “b” and times it by 1/30 s. The period is around 0.01 s,which means the light flicker frequency F is around 100 Hz.

Step 1307: Check the relationship of light flicker frequency and videoscanning frequency.

As mentioned above, there are three cases. When falling into case 1,that is, the light flicker frequency F is a multiple of the videoscanning frequency f (step 1309), the video scanning frequency f can bechanged (1311) and then the relationship of light flicker frequency andvideo scanning frequency can be checked again (step 1307).

When falling into case 2, that is, the light flicker frequency F is nota multiple of the video scanning frequency f, but both of them can bedivided by a constant number (step 1313), in other words, both of themare multiples of the same number, more videos can be taken and/or morefixed points in the frames of the videos can be made (step 1315).

When falling into case 3, that is, the light flicker frequency F is nota multiple of the video scanning frequency f, and both of them cannot bedivided by a constant number, the waveform can be reconstructed (step1317).

In this embodiment, as an example, the brightness pattern of frame 1, 2and 3 are different, but start to repeat after the 3^(rd) frame, whichmeans the brightness pattern of frame 1 is the same as that of frame 4,7, 10, 13, 16, 19, 22, 25, 28, the brightness pattern of frame 2 is thesame as that of frame 5, 8, 11, 14, 17, 20, 23, 26, 29 and thebrightness pattern of frame 3 is the same as that of frame 6, 9, 12, 15,18, 21, 24, 27, 30.

It falls into case 2 as mentioned above:

F/f=100/30;

F/f=10/3;

the denominator is 3, thus after 3 frames, the brightness pattern willstart to repeat.

Step 1315 (taking more videos and define more fixed points in the framesof the video) is executed in this case. Referring to FIG. 15, five morevideos can be taken and five fixed reference points (A, B, C, D and E)in the frames of the 5 video can be defined. Thus for point A, 15 setsof brightness and time location values from the 5 videos can becollected. For point B, another 15 sets can be got, and same as point C,D and E. As a result, after doing normalization of all the points, 75sets of brightness and time location values can be achieved.

Then step 1321 (reconstructing the brightness waveform) is executed. Asshown in FIG. 16, the brightness waveform of the light flicker isreconstructed. Some of the brightness and time location values mayoverlap. In this case, the average value of them can be taken.

After that step 1319 (checking if brightness waveform can bereconstructed or not) is executed. In this case, the brightness waveformcan be reconstructed, and the process ends at step 1323.

After reconstructing the brightness waveform, the flicker metrics can becalculated: flicker percentage and flicker index to determine whetherthe light flicker is severe or not. When taking videos, there exist somebackground noises. Those noises include other background light sourcesand the vibration of the digital or smartphone camera. However, they canbe filtered out by noise filtering technology. It is understood themethod for detecting electronic lighting flickering provided by theabove embodiments can be implemented by a mobile device, such as amobile phone or tablet, a digital camera, a programmed computer and etc.

While the present patent application has been shown and described withparticular references to a number of embodiments thereof, it should benoted that various other changes or modifications may be made withoutdeparting from the scope of the present invention.

What is claimed is:
 1. A method for detecting electronic lightingflickering, the method comprising: taking a video, with a duration of apredetermined period and a scanning frequency, of an electronic light;extracting a predetermined number of frames of pictures from the video;determining a flickering frequency of the electronic light based onnumber of pixels between two consecutive bright lines in each frame,number of pixels across the frame, and time period for which the frameis captured; determining at least one fixed reference point at eachframe; reconstructing a brightness waveform of the electronic light fromthe reference point in all frames of the video based on brightness valueof the reference point in each frame and time location value of thereference point in each frame; and determining relationship between theflickering frequency of the electronic light and the scanning frequencyof the video; wherein: if the flickering frequency is a multiple of thescanning frequency, the video is retaken with a different scanningfrequency; and if both the flickering frequency and the scanningfrequency are multiples of a same number, additional videos of theelectronic light are taken or number of the reference points isincreased.
 2. The method for detecting electronic lighting flickering ofclaim 1, wherein the flickering frequency of the electronic light isdetermined based on a flickering period, the flickering period beingdetermined based on ratio of the number of pixels between twoconsecutive bright lines or dark lines in each frame and the number ofpixels across the frame, multiplied by the time period for which theframe is captured.
 3. The method for detecting electronic lightingflickering of claim 2, wherein the time location value of the referencepoint in each frame is determined based on ratio of number of pixelsbetween the reference point and a bright line next to the referencepoint and the number of pixels between two consecutive bright lines inthe frame, multiplied by the flickering period.
 4. The method fordetecting electronic lighting flickering of claim 1, wherein ifadditional videos of the electronic light are taken, starting point ofthe brightness waveform of one video is different from that of anothervideo.
 5. A method for detecting electronic lighting flickering, themethod comprising: taking a video, with a duration of a predeterminedperiod and a scanning frequency, of an electronic light; extracting apredetermined number of frames of pictures from the video; determining aflickering frequency of the electronic light; determining at least onefixed reference point at each frame; and reconstructing a brightnesswaveform of the electronic light from the reference point in all framesof the video, wherein the brightness waveform of the electronic light isreconstructed from the reference point in all frames of the video basedon brightness value of the reference point in each frame and timelocation value of the reference point in each frame; and the timelocation value of the reference point in each frame is determined basedon ratio of number of pixels between the reference point and a brightline next to the reference point and the number of pixels between twoconsecutive bright lines in the frame, multiplied by the flickeringperiod.
 6. The method for detecting electronic lighting flickering ofclaim 5, wherein the flickering frequency of the electronic light isdetermined based on number of pixels between two consecutive brightlines in each frame, number of pixels across the frame, and time periodfor which the frame is captured.
 7. The method for detecting electroniclighting flickering of claim 6, wherein the flickering frequency of theelectronic light is determined based on a flickering period, theflickering period being determined based on ratio of the number ofpixels between two consecutive bright lines or dark lines in each frameand the number of pixels across the frame, multiplied by the time periodfor which the frame is captured.
 8. The method for detecting electroniclighting flickering of claim 5 further comprising determiningrelationship between the flickering frequency of the electronic lightand the scanning frequency of the video.
 9. The method for detectingelectronic lighting flickering of claim 8, wherein if the flickeringfrequency is a multiple of the scanning frequency, the video is retakenwith a different scanning frequency.
 10. The method for detectingelectronic lighting flickering of claim 8, wherein if both theflickering frequency and the scanning frequency are multiples of a samenumber, additional videos of the electronic light are taken.
 11. Themethod for detecting electronic lighting flickering of claim 8, whereinif both the flickering frequency and the scanning frequency aremultiples of a same number, number of the reference points is increased.12. A method for detecting electronic lighting flickering, the methodcomprising: taking a video, with a duration of a redetermined period anda scanning frequency, of an electronic light, the video comprising apredetermined number of frames of pictures; determining a flickeringfrequency of the electronic light; determining at least one fixedreference point at each frame: determining relationship between theflickering frequency of the electronic light and the scanning frequencyof the video; and reconstructing a brightness waveform of the electroniclight from the reference point in all frames of the video based on thedetermined relationship, wherein if the flickering is a multiple of thescanning frequency, the video is retake with a different scanningfrequency.
 13. The method for detecting electronic lighting flickeringof claim 12, wherein the flickering frequency of the electronic light isdetermined based on number of pixels between two consecutive brightlines in each frame, number of pixels across the frame, and time periodfor which the frame is captured.
 14. The method for detecting electroniclighting flickering of claim 13, wherein the flickering frequency of theelectronic light is determined based on a flickering period, theflickering period being determined based on ratio of the number ofpixels between two consecutive bright lines or dark lines in each frameand the number of pixels across the frame, multiplied by the time periodfor which the frame is captured.
 15. The method for detecting electroniclighting flickering of claim 12, wherein the brightness waveform of theelectronic light is reconstructed from the reference point in all framesof the video based on brightness value of the reference point in eachframe and time location value of the reference point in each frame. 16.The method for detecting electronic lighting flickering of claim 15,wherein the time location value of the reference point in each frame isdetermined based on ratio of number of pixels between the referencepoint and a bright line next to the reference point and the number ofpixels between two consecutive bright lines in the frame, multiplied bythe flickering period.
 17. The method for detecting electronic lightingflickering of claim 12, wherein if both the flickering frequency and thescanning frequency are multiples of a same number, additional videos ofthe electronic light are taken or number of the reference points isincreased.